Sustained post‐seismic effects on groundwater flow in fractured carbonate aquifers in Central Italy. Issue 5 (10th December 2019)

• Record Type: Journal Article
• Authors: Mastrorillo, Lucia; Saroli, Michele; Viaroli, Stefano; Banzato, Francesca; Valigi, Daniela; Petitta, Marco
• Is Part Of: Hydrological processes. Volume 34:Issue 5(2020)
• Page Start: 1167
• Page End: 1181
• Publication Date: 2019-12-10
• Subjects: Central Italy -- discharge increase -- earthquakes -- fractured aquifer -- hydraulic barrier breaching -- permeability enhancement; Hydrology -- Periodicals; Hydrology -- Research -- Periodicals; Hydrologic models -- Periodicals; Hydrological forecasting -- Periodicals; 631.432
• DOI: 10.1002/hyp.13662
• Languages: English
• ISSNs: 0885-6087

Abstract

Abstract: A sustained increase in spring discharges was monitored after the 2016 Central Italy seismic sequence in the fractured carbonate aquifer of Valnerina–Sibillini Mts. The groundwater surplus recorded between August 2016 and November 2017 was determined to be between 400 and 500 × 10 6 m 3 . In fractured aquifers, the post‐seismic rise in spring discharges is generally attributed to an increase in bulk permeability caused by the fracture cleaning effect, which is induced by pore pressure propagation. In the studied aquifers, the large amount of additional discharge cannot only be attributed to the enhanced permeability, which was evaluated to be less than 20% after each main seismic event. A detailed analysis of the spring discharge hydrographs and of the water level at five gauging stations was carried out to determine the possible causes of this sudden increase in groundwater outflow. Taking into account the geological and structural framework, a conceptual model of a basin‐in‐series has been adopted to describe the complex hydrogeological setting, where the thrusts and extensional faults have clearly influenced the groundwater flow directions before and after the seismic sequence. The prevalent portion of the total post‐seismic discharge surplus not explained by the increase in permeability has been attributed to changes in the hydraulic gradient that caused seismogenic fault rupture and the disruption in the upgradient sector of the aquifer. The additional flow calculated through the breach of the pre‐existing hydrostructural barrier corresponds to approximately 470 × 10 6 m 3 . This value is consistent with the total discharge increase measured in the whole study area, validating the proposed conceptual model. Consequently, a shift in the piezometric divide of the hydrogeological system has been induced, causing a potentially permanent change that lowers the discharge amount of the eastern springs. Abstract : A significant increase of spring discharge has been monitored after the 2016 seismic sequence in carbonate fractured aquifer of Valnerina–Sibillini Mts. (Central Italy). This additional discharge has been partly attributed to the enhanced permeability due to fracture cleaning effects but mostly to the seismogenetic fault disruption in the upgradient sector of the aquifer. The rupture induced an additional flow through the breaching of the pre‐existing hydraulic barrier and a shift eastward of the piezometric divide.